ABB REC650 Applications Manual page 62

Section 3
REC650 setting examples
56
system. The neutral point resistor gives a 10 A ground-fault current during a zero
resistance ground-fault. This means that the resistance is
22000 / 3
= = W
R 1270
N
10
GUID-4ECDF824-B17E-436D-A668-ACA06BB375F7 V2 EN
The total zero sequence impedance of the 22 kV system is:
Z = 3R // j3X // — jX
0 N N C
As the Petersen coil is tuned the zero sequence impedance is:
Z = 3R Ω / phase
0 N
The residual voltage during a resistive ground-fault in the 22 kV system is:
V V
Phase 0
= =
V or
o
×
3 R
V
f
+ phase
1 1
Z
0
GUID-AD49C138-F37B-4690-9E37-BA2BAD678A17-ANSI V1 EN
In our case the requirement is that ground-faults with a resistance up to 5 000 Ω shall be
detected. This gives:
V 1
0
= =
0 20 .
×
3 5000
V
+
phase 1
×
3 1270
GUID-42D376ED-052F-4E9B-B4D9-8D679127BC0C-ANSI V1 EN
Step 1 and step 2 is given the same voltage setting but step 2 shall have longer time delay.
The residual ground-fault protection shall have a definite time delay. The time setting is
set longer than the time delay of the ground-fault protection of the outgoing feeders having
maximum 2 s delay. The time delay for step 1 is set to 3 s and the time delay for step 2 is
set to 4 s.
1. Set GlobalBaseSel to 2
The (LV) winding data should be related to Global base 2.
2. Set Characterist1 to Definite time
3. Set Pickup1 to 20 % of VBase
4. Set t1 to 3.0 s
5. Set Pickup2 to 20 % of VBase
6. Set t2 to 4.0 s
Ω / phase
1
×
3 R
f
+
Z
0
1MRK 511 286-UUS A
(Equation 18)
(Equation 19)
(Equation 20)
Application manual